I. Field of the Invention
The present invention is directed generally to the field of sophisticated, high velocity, large or medium caliber projectile ammunition and, more particularly, improvements in the manufacture of segmented slab or disk material for use in a propellant system in the form of an ordered series of shaped slabs or disks. The use of such shapes leads to a more efficient use of propellant load space, reduces loading labor and overall cost, yet uses highly accurate propellant geometry to produce better, more uniform burning progressivity and increase propellant load leading to improved repeatability and more reliable and improved ballistic performance. Highly perforated propellant segments can be employed in the load to controllably increase burn rate and thereby increase overall propellant energy production efficiency.
II. Related Art
The evolution of large and medium caliber ordnance predictably has led to the development of increasingly sophisticated projectile rounds and firing systems. The use of smaller diameter projectiles together with discarding sabots to transfer momentum and velocity to the projectiles has led to the development of very high velocity (Mach V+) and highly accurate munitions. These sophisticated munitions also may contain highly sensitive target proximity detection devices which operate precision arming and detonating circuits. This allows the warhead to be detonated at or close to the most proximate approach to the target. In addition to the electric control and sensing improvements, the construction of the rounds themselves has undergone an evolution that has produced vastly improved capabilities in terms of the lethality produced by a single round on a target.
Conventional ammunition of the class described, such as that fired by military tank cannons, are typically breech loaded, electrically activated and fired from within the tank. The projectiles typically are electrically fired using a primer circuit which ignites a primer which, in turn, ignites a main propellant charge using DC voltage from a thermal battery. The projectile may contain electronics which utilize memory storage to operate a preprogrammed target acquisition or proximity system, and the arming and detonating devices in the shell during the flight of the shell. Then, it is apparent that large caliber ammunition, with respect to target acquisition, proximity detection, arming and detonating, has become very sophisticated. In addition, the projectiles themselves have become more aerodynamic and capable of traveling at speeds above Mach V.
While all these developments are interesting and important in the advancement of the art, the success of all ammunition projectiles still depends greatly upon the performance and the reproducibility of the performance of the associated propellant system.
Mass rate of gas generation is controlled by either physical or chemical means. While the development of new energetic formulations is on-going, many of these have problems meeting military specifications including insensitive munitions criteria. A variety of techniques have been tried in order to improve ammunition muzzle velocity performance by increasing propellant charge density, i.e., increasing the amount of propellant per available cartridge volume unit. These techniques have included utilizing various preformed shapes packed into the cartridge in an effort to increase density while minimizing adverse effects on burning rate. Such techniques have included the use of various sizes of granular extruded (short grain) propellant shapes, perforated stick extruded shapes which are long and cylindrically shaped and represent the most commonly used shapes. Another configuration is in the form of a rolled sheet of propellant. Bulk liquid propellants have also been used; however, they tend to burn in a non-reproducible manner and, therefore, results have been unpredictable.
In addition to the granular extruded (short grain) prior configuration, compressed granular solid and perforated extruded shapes have been used. While the extruded stick shape has increased projectile velocities, each stick has to be notched or "kerf cut" in several places on the side to prevent overpressurization during the burn. Stick and granular propellants are processed with 1, 7, 19 and 37 perforations (perf) to enhance progressivity. The 120 mm tank ammunition, for example, has evolved from 7-perf to 19-perf partial-cut (PC) stick and the stick propellant has also presented difficulties with respect to achieving high loading density. These factors make stick propellant more labor intensive than desired and difficult and costly to load in production.
With respect to processing, the propellant manufacturer making stick propellant must begin with carpet rolled propellant, extrude it with perforations, cut it to length, blend each length to minimize lot to lot performance variation, and kerf cut each length of stick before the propellant may be used.
The loading process for a cartridge using stick propellant is also very labor intensive and performance is not optimum because of problems mating surfaces of the sticks, as in the case of random placement with granular propellant. The method used to extrude both stick and granular propellant creates perforations during the process. However, dimensional variability is inherent in the extrusion process relative to the final web size and this reduces the propellant performance.
Repeatability of acceptable or good performance of stick propellant also requires uniformity of the notch or kerf size and web between the kerfs for proper burning. The current processes of extrusion and kerf cutting are rarely able to achieve this so that the sticks must be blended or mixed prior to loading to achieve some uniformity. The stick propellant, however, does give better performance than 19-perf granular propellant.
Another method utilizing ribbed sheet propellant rolled into cylindrical sections has been tested on smaller caliber ammunition. This method used longitudinal ribs replacing perforations to assist ignition. The rolled method experienced difficulty in conformance to the projectile geometry, poor progressivity, poor flame spread and poor ignition characteristics.
The provision of propellant segments in the form of disk or slab propellant shapes yields more efficient use of propellant load space and can achieve improved highly progressive burning and improved ballistic performance.
The slab loading can be parallel or perpendicular to the longitudinal axis of the munition, depending on the technique used. Typically, the disk load includes a plurality of ordered, serially stacked, relatively flat sided disk-shaped segments arranged perpendicular to the longitudinal axis of the cartridge or shell casing, each disk member having a large number of relatively small diameter perforations arranged in a predetermined pattern in accordance with aiding burn progression. The outside periphery of each disk is designed to conform to the inside diameter geometry of the shell casing. A central opening is provided in each disk to accommodate the primer tube, if used, or to match the outer configuration of the projectile in the upper portion of the cartridge.
Aligned openings may be provided in the disks in the form of cutouts to accommodate one or more alignment rods, which may be ignition sticks. If desired, propellant spacers in the form of thin propellant rings may be interleaved between disks to adjust burn progressivity or performance.
With respect to the slabs, a plurality of stacked, substantially rectangular, longitudinally dispersed flat shapes or slabs are employed parallel to the longitudinal axis of the cartridge casing. These are also suitably shaped internally and externally and perforated and provided with interslab openings as required to produce the desired burn performance. The segments of propellant may vary in thickness from about 0.15 centimeters to about 2.54 centimeters as ballistics and propellant progressivity requires. More details regarding slab and disk propellant arrangements can be found in co-pending application Ser. No. 08/537,882 U.S. Pat. No. 5,712,445, Issued Jan. 27, 1998) to Kassuelke et al, filed Apr. 10, 1996 and assigned to the same assignee as the present application. The entire contents of that patent are hereby incorporated by reference herein for any purpose.
It has been found that if the segments are provided with a relatively dense pattern of small bore perforations that are perpendicular to the faces of the slabs, this ensures that the individual slab burns in a highly progressive manner. The perforated slab arrangement does increase propellant progressivity and correspondingly increases the velocity of a 120 mm tank round by more than five percent (5%) over a conventional 19-perf PC stick propellant round. In this highly developed art, this is a significant advantage.
However, while the performance of the perforated slab system offers significant superiority over the stick or granular propellant, no practical method of commercially feasible manufacture has been successfully developed. And, accordingly, such would fulfill a definite need in the art.
Accordingly, a primary object of the present invention is to provide an improved process for producing punched (perforated) disk or slab propellant.
Another object of the invention is to provide a practical means for automating the production of punched disk or slab propellant.
A still further object of the invention is to provide a punching or perforating step which uses a special punch die assembly and automated indexing to provide a desired dense regular perforation pattern in slab or disk propellant.
Yet another object of the invention is to provide a method of making a propellant which produces a highly accurate, repeatable geometry, thereby increasing load density and reducing loading time.
A yet still further object of the present invention to produce a propellant which results in an increased charge load with a highly repeatable high burning rate achieved at a lower production cost.
Yet still another object of the invention is to provide slab or disk propellant having a sophisticated, repeatable perf pattern that enhances the burning performance of the material and the performance of an associated round.
Other objects and advantages will appear to those skilled in the art in connection with increased familiarity with the description and accounts, together with the drawing figures contained in the specification.